The ultimate aim is to produce an objective test of the adequacy of cognitive functions in infants and children. This test would then be applied to clinical populations in an effort to identify specific deficiencies responsible for their failure to learn, to communicate, or to conceptualize. The immediate objective is to describe the responses evoked from the normal brain by interesting visual and auditory stimuli. To this end children wearing conventional EEG electrodes will be exposed, in a home-like atmosphere, to pictures (presented by TV and slide-show displays); the cortical responses time-locked to these stimuli will be computer-extracted by conventional methods. In a similar way, time-locked auditory responses to "interesting" sounds (speech and non-speech) will be collected. These responses will be examined for the presence of a large negative wave with a latency around 500 msec (rather than, as in adults, a 300 msec positive wave) which was recently discovered in the cortical response evoked from children by such stimuli. The first phase of the study would accomplish a systematic description of this phenomenon in children between ages 1 year and 10 years. The second phase would compare this late wave response with other known measures (looking-time, heart rate change) of interest and attention in children. The final phase would collect evoked responses from appropriate clinical groups, identify the differences between their responses and those of the normal group, and construct a test battery that will distinguish them from normal children on this basis.